Digestion & Respiration

The last set of notes for the year left me feeling happy and raring to go for another year. Again this seems like a revision of primary school materials, but I'm not complaining. Something that I had not thought of before was the question: Why does the stomach not "digest" itself? Something seemingly devilishly simple gave me a lot of food for thought. It turns out that there is a layer of mucus protecting the stomach from the hydrochloric acid. Respiration was pretty much just the difference between it and breathing. We also compared it with photosynthesis in which one uses oxygen and produces carbon dioxide while the other is the opposite. There was also other criteria while the only two similarities were that both involve energy and enzymes. Our teacher did not really go through everything so detailed as we had learnt this before.